Several changes in the sequence of the gene encoding sterol 14alpha-demethylase were found that have been described in other fungi as being correlated with resistance to azole fungicides. No correlation was found between gene expression and propiconazole resistance.

Benzimidazoles are systemic fungicides widely used for the control of Black Sigatoka. They exert their antifungal activity by binding to b-tubulin and disrupting fungal cell division. The specific mode of action of benzimidazoles, along with their intensive use, has favoured the appearance of resistance in Mycosphaerella fijiensis, a situation which has precluded their use in several countries. Studies made in different fungi have identified several single nucleotide polymorphisms (SNP) associated with resistance to these fungicides. Despite the economic importance of this disease and the appearance of resistance to benzimidazoles, studies of the molecular mechanisms involved in resistance of this fungus have not been carried out. In this study, a fragment of the b-tubulin gene of 10 M. fijiensis isolates with three different levels of resistance to benomyl, was amplified and sequenced. The analysis of the sequences showed a change of adenine instead of cytosine in codon 198 of all the b-tubulin genes obtained from the isolates classified as having medium or high resistance. The single nucleotide change found, allowed the development of a molecular method based on polymerase chain reaction amplification and restriction digestion, which is able to differentiate resistant from susceptible isolates. The method was validated on a total of 44 isolates collected from different regions from Colombia, showing a 100% correlation between the presence of the resistant allele and the ability of the fungal isolate to grow in at least 10 lg a.i./ml benomyl. This method will be a valuable tool for monitoring benomyl resistance in M. fijiensis.www.blackwell-synergy.com

Genetic diversity of avocado (Persea americana Mill) cultivars in Antioquia, Colombia. The aim of this work was to characterize 111 native avocado (Persea americana Mill) cultivars with molecular and morphological markers. This study was carried out from 2009 to 2011 at Antioquia Department, Colombia, South America. The molecular analysis was performed with 38 AFLP (amplified fragment length polymorphism) and the primers E-ACT/M-CTC and E-AAC/M-CAA, that produced high levels of expected hetorozygocities for avocado from the municipalities of Valparaíso, Santa Bárbara and La Ceja. The native cultivars obtained from these places showed 100% genetic similarity with Hass. Twenty three shared AFLP loci where observed among all native genetic material and Hass, Fuerte and Reed from Antioquia. A UPGMA (Unweighted Pair Group Method with Arithmetic Mean) dendrogram constructed with the AFLPs and Nei genetic distance produced three clusters that grouped individuals that are geographically close and in places climatically similar. In addition, a principal components analysis (PCA) based on morphological traits produced three groups that are coincident with the dendrogram. The AMOVA (Analysis of Molecular Variance) estimated a significant but low Phipt (Fst analogous) value, indicating genetic differentiation among the Antioquia avocados. The results obtained in this work identified zones of Antioquia with native material that could potentially be used as injertation for the Hass variety, as a first step towards certification of avocado vegetative material in Colombia.

Grafting induces precocity and maintains clonal integrity in fruit tree crops. However, the complex rootstock × scion interaction often precludes understanding how the tree phenotype is shaped, limiting the potential to select optimum rootstocks. Therefore, it is necessary to assess (1) how seedling progenies inherit trait variation from elite ‘plus trees’, and (2) whether such family superiority may be transferred after grafting to the clonal scion. To bridge this gap, we quantified additive genetic parameters (i.e., narrow sense heritability—h2, and genetic-estimated breeding values—GEBVs) across landraces, “criollo”, “plus trees” of the super-food fruit tree crop avocado (Persea americanaMill.), and their open-pollinated (OP) half-sib seedling families. Specifically, we used a genomic best linear unbiased prediction (G-BLUP) model to merge phenotypic characterization of 17 morpho-agronomic traits with genetic screening of 13 highly polymorphic SSR markers in a diverse panel of 104 avocado “criollo” “plus trees.” Estimated additive genetic parameters were validated at a 5-year-old common garden trial (i.e., provenance test), in which 22 OP half-sib seedlings from 82 elite “plus trees” served as rootstocks for the cv. Hass clone. Heritability (h2) scores in the “criollo” “plus trees” ranged from 0.28 to 0.51. The highesth2values were observed for ribbed petiole and adaxial veins with 0.47 (CI 95%0.2–0.8) and 0.51 (CI 0.2–0.8), respectively. Theh2scores for the agronomic traits ranged from 0.34 (CI 0.2–0.6) to 0.39 (CI 0.2–0.6) for seed weight, fruit weight, and total volume, respectively. When inspecting yield variation across 5-year-old grafted avocado cv. Hass trees with elite OP half-sib seedling rootstocks, the traits total number of fruits and fruits’ weight, respectively, exhibitedh2scores of 0.36 (± 0.23) and 0.11 (± 0.09). Our results indicate that elite “criollo” “plus trees” may serve as promissory donors of seedling rootstocks for avocado cv. Hass orchards due to the inheritance of their outstanding trait values. This reinforces the feasibility to leverage natural variation from “plus trees”viaOP half-sib seedling rootstock families. By jointly estimating half-sib family effects and rootstock-mediated heritability, this study promises boosting seedling rootstock breeding programs, while better discerning the consequences of grafting in fruit tree crops.

In this study, the genetic diversity of 90 avocado (Persea americana Mill) cultivars from Antioquia (Colombia) was compared to 67 germplasm collection accessions using 14 microsatellites. An average of 4.32 ± 2.0 alleles per locus was found, as observed in previous studies. The expected and observed heterozygosity ranges were 0.384-0.724 and 0.393-0.686, respectively. The Antioquian avocados were genetically structured according to an analysis of molecular variance test (fixation index (F ST) = 0.054, P < 0.00001). An unweighted pair group method with arithmetic mean (UPGMA) dendrogram with F ST paired data produced 2 clusters: one composed by Antioquian avocados and the other by the germplasm collection. Another UPGMA dendrogram with individual Nei-Li distances and additional STRUCTURE analysis separated the Antioquian avocados into 3 clusters (K = 3). Combining samples from the Colombian and germplasm collections produced K = 2. Genetic differentiations between the Antioquian and worldwide avocado germplasm collection could be due to crosses within the Antioquian avocados having been enhanced by insect pollinators, whereas avocados stored in the germplasm collection were constituted by cultivars with known genetic origins. Findings from this study demonstrated that criollo avocado genetics are unique in Antioquia, since the species has been naturally crossed in the field and its closest accession is from Guatemala. Nevertheless, it is important to continue genotyping this species in other locations in Colombia from Sylvester and cultivar populations of this crop to determine its origin.